Different regional changes of fluorescence spectra of clear human lenses and nuclear cataracts

Fluorescence spectra are recorded from the cortex and nucleus of the same human lenses [clear and cataracta brunescens (nigra) with colorless cortex]. When comparing clear cortices with either the harder nucleus of a clear lens, or a cataracta brunescens for a given excitation wavelength, a shift of the fluorescence maxima of the nucleus to longer wavelengths is observed. The shift appears to be independent of the degree of coloring since it is very similar for different nuclei, and it is not increased in cataracta nigra. The fluorescence intensities are similar when comparing the clear cortex of clear lenses and cataracta brunescens. For the nuclei, however, the intensity increases by up to four to six times with increasing coloring. For constant excitation wavelength, the fluorescence band maximum of the nucleus (of clear lenses and of cataracta brunescens) exhibits roughly the same shift to longer wavelengths as that of the cortex. Upon 320 nm excitation the fluorescence intensity of a cataracta nigra is about twice that of a clear lens of juvenile age. Upon 380 nm excitation the factor increases to four. Therefore in older and colored lens nuclei a red shift of the fluorescence maximum with increasing excitation wavelength is observed. We discuss whether or not the changes in the molecular proteins, in addition to advanced glycolization end products, may be responsible for the different fluorescence properties (and the brown color) with increasing age.